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magnetic and electric characteristics and abnormality of low-temperature resistivity in La_(0.67–x)Er_xSr_(0.33)MnO_3(0.00≤x≤0.20) system

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Journal of Rare Earths 2009年第5期27卷 834-838页

作者：刘宁严国清张明玉 Anhui Key Laboratory of Spin Electron and Nanomaterials Suzhou College College of Science Anhui Science and Technology University National Laboratory of Solid State Microstructures Physics DepartmentNanjing University

M-T curves, ρ-T curves, and MR-T curves of La0.67-xErxSr0.33MnO3(x=0.00, 0.10, 0.20) system were studied by experiments. The experiments showed that: with increasing the doping amount, the magnetic structure of the system transformed from long-range ferromagnetic ordering to spin-cluster glass state, and M-T curves bent up in the extremely low temperature range; the resistivity of the system increased with increasing doping amount and exhibited the minimum phenomenon of low-temperature resistivity. The variation of the magnetic and electric properties came from the extra magnetic coupling induced by the doping and from the Kondo effect induced by the lattice distortion and local magnetic moments which was similar to that induced by the scattering of magnetic impurities on electron spins. © 2009 The Chinese Society of Rare Earths.

关键词： Condensed matter physics Electric resistance Erbium Impurities Kondo effect magnetic couplings magnetic moments magnetic structure Manganese compounds Rare earths Solids Spin dynamics Spin glass

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Spontaneous Emission of a Two-Level Static Atom Coupling with Electromagnetic Vacuum Fluctuations Outside a High-Dimensional Einstein Gauss-Bonnet Black Hole

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Chinese Physics Letters 2014年第10期31卷 5-9页

作者：张明杨战营岳瑞宏 School of Physics Northwest University Xi'an 710069 Faculty of Science Ningbo University Ningbo 315211

Using the generalized formalism of Dalibard, Dupont-Roc and Cohen-Tannoudji we investigate the spontaneous excitation of a static atom interacting with electromagnetic vacuum fluctuations outside an Einstein Gauss-Bonnet black hole in d-dimensions. It shows that spontaneous excitation does not occur in a Boulware vacuum, while exists in an Unruh vacuum and Hattie-Hawking vacuum. As to the total rate of change of the atomic energy, it does not receive the contribution from the coupling constant of the Gauss-Bonnet term at spatial infinity, only the dimensional parameter has the contribution to it. Near the event horizon, both the coupling constant and the dimension p contribute to the total rate of change of the atomic energy in all three kinds of vacuum. We discuss the contribution of the coupling constant and dimensional factor to the results in three different kinds of spacetime lastly.

关键词： SPONTANEOUS emission FLUCTUATIONS (Physics) magnetic couplings GAUSS-Bonnet theorem ELECTROmagnetic pulses VACUUM-gages

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Nonlinear Control of magnetically-geared Drive-trains

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International Journal of Automation and computing 2013年第4期10卷 319-326页

作者： Ryan Montague Chris Bingham Department of Computer Science University of York School of Engineering University of Lincoln

The paper considers certain impedimental issues related to the use of magnetic gearbox and magnetic coupling technologies in high performance servo control systems. A prototype magnetic coupling is used as a basis for demonstrating that the underlying torque transfer characteristic is significantly nonlinear when transmitted torque approaches the maximum designed pull-out torque of the device. It is shown that linear controllers for speed control proportional plus integral （PI） and position control proportional plus derivative （PD） result in acceptable performance provided the magnetic coupling operates below 80 % of designed pull-out torque. To fully compensate for the inherent nonlinearity of the torque transfer characteristic, feedback linearizing control laws and state transformations are derived resulting in exactly linear input-output characteristic for position and speed control of magnetically-geared drive-trains. With the addition of state feedback, the closed-loop dynamics for both position and speed control of a magnetically-geared drive-train can be designed to satisfy the integral of time multiplied by absolute error （ITAE） optimized linear response for a step input. Outstanding results are demonstrated through simulation and experimental real-time implementation on a demonstrator magnetically-geared drive-train.

关键词： magnetic gears magnetic couplings linear control nonlinear control feedback linearization.

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Coexistence of Two Mechanisms for Extracting Energy from a Rotating Black Hole

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Chinese Physics Letters 2003年第9期20卷 1644-1647页

作者：马任意汪定雄雷卫华 DepartmentofPhysics HuazhongUniversityofScienceandTechnologyWuhan430074 Towhomcorrespondenceshouldbeaddressed.

Evolution characteristics of a rotating black hole (BH) are discussed in coexistence of the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process in the parameter space consisting of the BH spin and the power-law index of the magnetic field on the disc. The condition for the coexistence of the two energy mechanisms are derived by using the mapping relation between the angular coordinate on the BH horizon and the radial coordinate on the disc. It is shown that not only the two mechanisms can coexist, but also the power and the rate of change of BH entropy in the BZ process will dominate over those in the MC process, provided that the BH spin and the power-law index are great enough.

关键词： magnetic couplings

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Effects of magnetic Coupling of Temperature Profile of Black—Hole Accretion Disc

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Chinese Physics Letters 2002年第2期19卷 276-279页

作者：雷卫华汪定雄等 DeprtmentofPhysics HuazhongUniversityofScienceandTechnologyWuhan430074

We propose a model of the magnetic coupling (MC) of a rotating black hole (BH) with the surrounding accretion disc in order to study the radial temperature profile in the inner region of the disc, in which a linear map from the angular coordinate on the BH horizon to the radial coordinate on the thin disc is given by closed magnetic field lines. The MC power and torque are derived using a modified equivalent circuit. It is shown that the MC effects on the temperature profile are related intimately to the BH spin, resulting in the variation of the value and the position of the peak temperature. It turns out that the value range of the colour temperature of the disc is extended by the MC effects

关键词： magnetic couplings

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